Complete Calculations of Wbb̄ and Wbb̄ + jet Production at Tevatron and LHC: Probing Anomalous Wtb Couplings in Single Top Production

We present the results of a complete tree level calculation of the processes pp(p̄) → Wbb̄ and Wbb̄ + jet that includes the single top signal and all irreducible backgrounds simultaneously. In order to probe the structure of the Wtb coupling with the highest possible accuracy and to look for possible deviations from standard model predictions, we identify sensitive observables and propose an optimal set of cuts which minimizes the background compared to the signal. At the LHC, the single top and the single anti-top rates are different and the corresponding asymmetry yields additional information. The analysis shows that the sensitivity for anomalous couplings will be improved at the LHC by a factor of 2–3 compared to the expectations for the first measurements at the upgraded Tevatron. Still, the bounds on anomalous couplings obtained at hadron colliders will remain 2–8 times larger than those from high energy γe colliders, which will, however, not be available for some time. All basic calculations have been carried out using the computer package CompHEP. The known NLO corrections to the single top rate have been taken into account.